Enzymatic synthesis of the alpha 3-galactosyl-Lex tetrasaccharide: a potential ligand for selectin-type adhesion molecules.

Using recombinant UDP-Gal:Gal beta 1-->4GlcNAc alpha 1,3-galactosyltransferase and human milk alpha 1,3-fucosyltransferase the disaccharide Gal beta 1-->4GlcNAc has been converted in vitro into a tetrasaccharide product. The product has been characterized by gel filtration chromatography and HPLC and was analyzed using 1H-NMR. Based on NMR spectral data along with the known linkage specificity of the alpha 1,3-galactosyltransferase and the alpha 1,3-fucosyltransferase used, the chromatographic behaviour of the product, and the 1:1 molar ratios of the galactose and fucose residues calculated from incorporated radioactivity, it is concluded that the structure of the tetrasaccharide product is Gal alpha 1-->3Gal beta 1--4[Fuc alpha 1-->3]-GlcNAc. The tetrasaccharide is a non-charged analogue of the sialyl-Lex determinant that potentially may act as a ligand structure in selectin-mediated cell-cell adhesion.